about summary refs log tree commit diff
path: root/sysdeps
diff options
context:
space:
mode:
authorJoseph Myers <joseph@codesourcery.com>2014-06-24 21:00:08 +0000
committerJoseph Myers <joseph@codesourcery.com>2014-06-24 21:00:08 +0000
commit4060283decf711ed95a6c4993ffeaba39f8cd40a (patch)
treed303f8bcf7bd9fafbbb5edddc48c7c2be827f84e /sysdeps
parente7dd3c8c1db8c6d293abb995e033893b7328ad19 (diff)
downloadglibc-4060283decf711ed95a6c4993ffeaba39f8cd40a.tar.gz
glibc-4060283decf711ed95a6c4993ffeaba39f8cd40a.tar.xz
glibc-4060283decf711ed95a6c4993ffeaba39f8cd40a.zip
Fix x86/x86_64 expm1l spurious underflow exceptions (bug 16539).
This patch fixes bug 16539, spurious underflow exceptions from x86 /
x86-64 expm1l.  The problem is that the computation of a base-2
exponent with extra precision involves spurious underflows for
arguments that are small but not subnormal, so a check is added to
just return the argument in those cases.  (If the argument *is*
subnormal, underflowing is correct and the existing code will always
underflow, so it suffices to keep using the existing code in that
case; some expm1 implementations have a bug (bug 16353) with missing
underflow exceptions, but I don't think there's such a bug in this
particular version.)

Tested x86_64 and x86; no ulps updates needed.

(auto-libm-test-out diffs omitted below.)

	[BZ #16539]
	* sysdeps/i386/fpu/e_expl.S (IEEE754_EXPL) [USE_AS_EXPM1L]: Just
	return the argument for normal arguments with exponent below -64.
	* sysdeps/x86_64/fpu/e_expl.S (IEEE754_EXPL) [USE_AS_EXPM1L]:
	Likewise.
	* math/auto-libm-test-in: Add another test of expm1.
	* math/auto-libm-test-out: Regenerated.
Diffstat (limited to 'sysdeps')
-rw-r--r--sysdeps/i386/fpu/e_expl.S10
-rw-r--r--sysdeps/x86_64/fpu/e_expl.S10
2 files changed, 20 insertions, 0 deletions
diff --git a/sysdeps/i386/fpu/e_expl.S b/sysdeps/i386/fpu/e_expl.S
index eb4086b3f5..c7e43732dc 100644
--- a/sysdeps/i386/fpu/e_expl.S
+++ b/sysdeps/i386/fpu/e_expl.S
@@ -108,6 +108,16 @@ ENTRY(IEEE754_EXPL)
 	andb	%ah, %dh
 	cmpb	$0x40, %dh
 	je	2f
+
+	/* Test for arguments that are small but not subnormal.  */
+	movzwl	4+8(%esp), %eax
+	andl	$0x7fff, %eax
+	cmpl	$0x3fbf, %eax
+	jge	3f
+	/* Argument's exponent below -64; avoid spurious underflow if
+	   normal.  */
+	cmpl	$0x0001, %eax
+	jge	2f
 #else
 	movzwl	4+8(%esp), %eax
 	andl	$0x7fff, %eax
diff --git a/sysdeps/x86_64/fpu/e_expl.S b/sysdeps/x86_64/fpu/e_expl.S
index 338527b3de..0ebe3882a5 100644
--- a/sysdeps/x86_64/fpu/e_expl.S
+++ b/sysdeps/x86_64/fpu/e_expl.S
@@ -105,6 +105,16 @@ ENTRY(IEEE754_EXPL)
 	andb	%ah, %dh
 	cmpb	$0x40, %dh
 	je	2f
+
+	/* Test for arguments that are small but not subnormal.  */
+	movzwl	8+8(%rsp), %eax
+	andl	$0x7fff, %eax
+	cmpl	$0x3fbf, %eax
+	jge	3f
+	/* Argument's exponent below -64; avoid spurious underflow if
+	   normal.  */
+	cmpl	$0x0001, %eax
+	jge	2f
 #else
 	movzwl	8+8(%rsp), %eax
 	andl	$0x7fff, %eax